Field
Multi-chip product cooling.
Description of Related Art
Many integrated circuit products incorporate multi-chip products. An example of a multi-chip product is a package including a microprocessor and memory and companion devices or components (e.g., chips). Packaging can consist of a single integrated heat spreader (IHS) over all the components or individual IHS for each component. Each packaging option has advantages and disadvantages but still each component requires adequate cooling.
The different package options significantly impact the overall junction to ambient thermal resistance. A bond line thickness (BLT) of each of a thermal interface material between the die and IHS (TIM1) and thermal interface material between the IHS and heatsink (TIM2) are two of the most significant thermal resistance factors along with die/IHS size, power density, and total power.
A single IHS design provides one relatively flat surface to interface with a cooling solution such as a passive heat exchanger (e.g., a heatsink) but a single IHS package option can have significant implications on the TIM1 BLT and thus the package thermal resistance (die to IHS). The tolerance between each component must be accounted for either at the package level internal to the IHS as in the single IHS option or at the cooling solution level with the individual IHS option. The tolerance results in a wide range of thickness for the TIM1 BLT of certain chips in a multi-chip product employing the single IHS option. As companion components decrease in size and increase in power density, the thermal resistance from the TIM1 BLT can significantly impact the package performance.
The individual IHS package option minimizes the TIM1 BLT on each component and thus also a package thermal resistance. One drawback is that there are now multiple non-coplanar surfaces that must interface to the cooling solution. The cooling solution (passive heat exchanger) is typically justified to the CPU IHS thus minimizing its TIM2 BLT and corresponding thermal resistance. But the cooling must now account for the variation and non-planarity of each individual component IHS often resulting in a large TIM2 BLT range on each component.